<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>基本数据类型</title>
</head>

<body>
  <script>
    /*
    基本数据类型
      number
      string
      Boolean
      undefined
      null

      引用数据类型
      object
      function
      array
    */
    // 取余
    document.write('余数是' + 3 % 5 + '<br>')
    // console.log(3 % 4);

    let r = prompt('请输入圆的半径')
    let π = 3.14
    document.write('圆的面积是' + π * r * r)
  </script>
</body>

</html>